1. Field of the Invention
The present invention relates to an in-vehicle electronic control unit furnished with a fuel evaporation preventing function of preventing diffusion of fuel evaporation emission when the vehicle is refueled, and more particularly, to an in-vehicle electronic control unit that prevents overdischarge of an in-vehicle battery when a filler cap provided to close a filler neck or a filler lid provided as a safety door is left open.
2. Description of the Related Art
Regarding an in-vehicle fuel tank storing fuel for an in-vehicle engine, various preventive measures have been taken to prevent evaporated fuel accumulated in the fuel tank from being discharged to the atmosphere when a filler cap put on a filler neck of the fuel tank is opened to refuel a vehicle.
For example, according to Japanese Patent No. 2538101 (Patent Document 1), a switch to detect opening and closing states is provided to each of a filler cap and a filler lid as a safety door of the filler cap. Also, a check valve and a bypass solenoid valve are provided to an evaporation tube connecting a fuel tank and a canister. When both the filler cap and the filler lid are closed while the vehicle is in motion and when both the filler cap and the filler lid are opened while the vehicle is refueled, the solenoid valve is closed by energizing a solenoid. When the vehicle is refueled, the solenoid valve is opened by de-energizing the solenoid in a transition period during which the filler lid is opened first but the filler cap is not opened yet. Consequently, because evaporated fuel in the fuel tank is introduced into the canister via a bypass channel by way of the evaporation tube, the evaporated fuel is not forced out to the atmosphere by an internal pressure of the fuel tank when the filler cap is opened. Air pollution can be therefore prevented.
According to Japanese Patent No. 2962166 (Patent Document 2), when a refuel switch is operated before the vehicle is refueled, a solenoid valve provided to a pipe connecting a fuel tank and a canister is opened and a compressor starts to operate under the control of an electronic control unit, so that fuel evaporation emission in the fuel tank is sent into a reservoir via the pipe. Thereafter, when the internal pressure of the fuel tank detected by a pressure sensor drops to or below atmospheric pressure, the solenoid valve is closed and the compressor stops operating. A filler lid opening motor is then driven and the filler lid is opened so that the vehicle is refueled. Consequently, it becomes possible to prevent a discharge of fuel evaporation emission from the fuel tank when the vehicle is refueled.
According to Japanese Patent No. 4567534 (Patent Document 3), a vehicle control unit, which is a fuel control module controlling electrical components provided to a fuel supply system and installed separately from an engine control module controlling the engine, determines whether there is a refuel request to the fuel tank depending on whether a filler cap or a fuel filler lid is opened while the engine is at rest. When there is no refuel request, the vehicle control unit shifts to a low power consumption mode. The vehicle control unit resumes to a normal mode upon issuance of a refuel request and outputs a drive signal to open the solenoid valve so that the vehicle is refueled. Also, the vehicle control unit is forced to shift to the low power consumption mode when a refuel requesting state to the fuel tank continues for a predetermined time or longer. The low power consumption mode is a mode in which no control output is generated and a microcomputer is brought into a low power consuming state by lowering a clock frequency of a CPU and by actuating only a portion that reads an external signal and a portion that performs a communication function.
Patent Document 1: Japanese Patent No. 2538101 (Claim 1 and FIG. 1)
Patent Document 2: Japanese Patent No. 2962166 (Claim 2, Paragraph [0022], and FIG. 1)
Patent Document 3: Japanese Patent No. 4567534 (Claims 1 through 3, Paragraphs [0022] and [0023], and FIG. 1)
A fuel tank apparatus of Patent Document 1 de-energizes the solenoid upon occurrence of a contact failure in one of the filler lid switch and the filler cap switch under circumstances where the filler lid and the filler cap are closed and both the filler lid switch and the filler cap switch must be closed. Accordingly, the solenoid valve is opened constantly and there arises a fail-safe problem.
Under circumstances where the filler lid and the filler cap are closed and both the filler lid switch and the filler cap switch are closed normally, a pair of a relay and a solenoid is energized to close the solenoid valve constantly. Accordingly, a load current is flown into a pair of the relay and the solenoid while the vehicle is in a parked state and overdischarge occurs in the in-vehicle battery. Hence, there arises a problem in terms of power saving. The power saving problem may be solved by stopping power feeding to a pair of the relay and the solenoid when a power supply switch is opened. However, in order to refuel the vehicle while the power supply switch is opened, it is necessary to configure in such a manner that power is fed to a pair of the relay and the solenoid even when the power supply switch is opened. After all, the fuel tank apparatus is of a configuration that defies a solution of the power saving problem.
In a fuel evaporation preventing apparatus of Patent Document 2, a filler lid open command switch, a filler lid opening detection switch, various solenoid valves, and a filler lid opening motor are under the control of the electronic control unit. This configuration raises a problem that it is impossible to refuel the vehicle in a parked state. It should be noted, however, that the electronic control unit remains in an operating state and is capable of running a control program for preventing fuel evaporation while an ignition key is turned at an ON position and at least until a predetermined time (a time sufficiently longer than a maximum refuel time) elapses since the ignition key is turned OFF. However, when an individual wishes to perform a refuel operation after an elapse of the predetermined time, the ignition key has to be turned to the ON position first. Hence, the power supply may possibly be turned OFF during the refuel operation unless the predetermined time is sufficiently long. It therefore becomes necessary to feed the electronic control unit idly for a long time. Accordingly, in a case where a microprocessor is incorporated into the electronic control unit, it is required to use a low-power-consuming microprocessor having a small program memory capacity and operating at low speeds.
The vehicle control unit of Patent Document 3 uses two types of control modules that handle the same input and output signal. It is therefore necessary to exchange signals with each other and the fuel control module requires a complex microprocessor operating in two modes. Accordingly, there is a problem that it is necessary to constantly feed more modules even in a low power consumption mode. The engine control module normally incorporates a low-power-consuming soak timer circuit to detect fuel evaporation and the soak timer circuit is constantly fed from the in-vehicle battery.
The invention has an object to solve the problems discussed above and provides an in-vehicle electronic control unit capable of performing decompression processing of a fuel tank without requiring a new control unit so as to prevent diffusion of fuel evaporation emission from the fuel tank when a filler cap is opened.